Members of the civil defense search for bodies in the rubble of a building in the Mosul al-Jadida neighborhood of Mosul. (Alice Martins for The Washington Post)

The U.S. military acknowledged for the first time Saturday that it launched an airstrike against the Islamic State in the densely packed Iraqi city of Mosul, where residents say more than 100 people were killed in a single event.

If confirmed, the March 17 incident would mark the greatest loss of civilian life since the United States began strikes on Islamic State targets in Iraq and Syria in 2014.

An “initial review” showed that the coalition struck ISIS fighters and equipment in west Mosul at the request of Iraq forces and “at the location corresponding to allegations of civilian casualties,” the task force leading the coalition said in a statement.

Previously, the U.S.-led coalition had said officials were unsure whether there were any air attacks targeting the specific area of the neighborhood Mosul al-Jadida at the time when residents claim a strike killed 137 civilians.

Iraqi officials working on the rescue said they had pulled 83 bodies — including many women and children — from a destroyed building by sundown on Saturday. They have yet to complete excavations at the site.

The U.S. military is conducting an initial investigation into the incident.

In a statement U.S. Central Command said it had received multiple "conflicting allegations" placing a strike in the area sometime between March 17 and 23. (Loveday Morris/The Washington Post)

Allegations of large-scale civilian carnage deepen questions about the conduct of counterterrorism operations under President Trump, who promised to act more aggressively to stamp out militant groups but whose short presidency has been marked by a spate of high-profile incidents in which civilians may have died.

In addition to the March 17 strike in Mosul, the U.S. military is now investigating a separate attack this month alleged to have killed scores of civilians at a mosque in Syria. Military leaders have also acknowledged the death of at least some civilians in a Navy SEAL raid in Yemen in January.

Activists including Airwars, a U.K.-based monitoring group, have raised the alarm at what they say is a surge in U.S.-linked deaths in Iraq and Syria, asserting that 1,000 civilians have died this month alone in strikes by the U.S.-led coalition in Iraq and Syria.

While the Obama administration acknowledged that its military operations resulted in a number of civilian casualty incidents in Iraq and Syria and elsewhere, the tightly spaced series of recent allegations is striking.

It remains unclear what, if any, common factors may be behind the reported uptick in civilian bloodshed.

Operations against Islamic State strongholds have reached a new, more intense phase in Mosul, where local forces are battling militants in heavily populated neighborhoods, and in Syria, where the United States is seeking to deal a decisive blow to several militant groups.

In his first days in office, President Trump, who criticized his predecessor as weak against militant groups, asked the Pentagon to consider whether restrictions on U.S. military operations against the group, designed in part to protect civilian life, should be loosened.

Officials maintain that, so far at least, no changes to existing rules for military operations have taken place. Military commanders also say they take extensive measures to protect civilian life. In its statement, the U.S.-led coalition said its goal was “zero civilian casualties.”

“But the coalition will not abandon our commitment to our Iraqi partners because of ISIS’s inhuman tactics terrorizing civilians, using human shields, and fighting from protected sites such as schools, hospitals, religious sites and civilian neighborhoods,” the statement read.

Like other strikes conducted in support of Iraqi ground operations, the March 17 attack was approved at a U.S. command center either in Iraq or elsewhere in the Middle East, defense officials said. Typically, a one-star general or a team working under him or her reviews and approves such strikes. That makes them different from strikes targeting a specific individual, which are planned much farther in advance and could require approval from the White House.

The increase in civilian casualty claims threatens to tarnish the gains of Iraqi forces and the U.S.-led coalition. Analysts have said that with residents fed up after nearly three years of brutal Islamic State rule, the operation to retake the city presents an opportunity to reset relations between the majority Sunni city and the government in Baghdad — essential for preventing extremism.

But the extended operation to retake Islamic State’s last remaining stronghold in Iraq has turned into a messy battle, where civilians are caught in the crossfire.

Leaving the bombed-out street with tears in his eyes on Friday, Saban Ahmed Ibrahim was among those who claimed to have lost relatives in the strike. He said he moved his wife and two children — a two-year-old boy and a one-year-old girl — out of his neighborhood to shelter in Mosul al-Jadida because of the heavy fighting around his home. But after his neighborhood was retaken by Iraqi security forces, his family became trapped on the other side of the front line.

He was still waiting for the bodies of his loved ones to be recovered from the building.

“I blame everyone,” he said. “I still have God and I trust that he will take his revenge.”

Iraqi commanders have attempted to play down the incident and have restricted press access to the area. An Iraqi military commander suggested the large death toll in the March 17 incident may have been partially caused by the fact that a missile struck a car bomb, unleashing a giant explosion. Another suggested militants booby-trapped the building with explosives and detonated it.

However, several civil defense officials said that they could tell by the direction of the blast damage and the lack of a crater associated with a car bomb explosion that damage was caused by a direct airstrike on the property.

Rescue workers and residents described a hellish scene, where scores of civilians were killed in nearby buildings in heavy bombardment lasting several days. Other families on an adjacent street also alleged their houses were destroyed by airstrikes — killing scores more.

U.S. officials said it has been difficult to determine exactly what occurred because the same area appeared to have been hit with a number of strikes or explosions in the days surrounding the March 17 attack.

Islamic State fighters moved families into the area as they used it to launch attacks on the advancing Iraqi forces, residents said. They said ISIS is also forcing residents to leave their front doors open, so the fighters can move from house to house easily.

Residents said the house was packed with several families because it was one of the few in the area with a basement during the heavy fighting. An Islamic State headquarters was discovered in a building nearby.

“They have a new style of fighting, which is a heinous one,” said Iraqi counterterrosim commander Lt. Gen. Abdul Ghani al-Assadi. “They gather civilians into a house where they are fighting so we will request an airstrike and then they will die with the civilians,” he said, but claimed the mass casualty incident in Mosul al-Jadida was caused by an Islamic State car bomb detonating.

Relatives and rescue workers have been picking through debris in the neighborhood for days, pulling out corpses and lifting them into blue body bags for burial.

Rescue efforts were initially hampered by a lack of security, and poorly equipped civil defense teams. Extra workers were sent from Baghdad to assist, but by the time they arrived in the neighborhood five days after the strikes, hope of finding anyone alive had dimmed.

“Islamic State is gathering people and using them as shields and the coalition comes and bombs — they are both to blame,” said Moataz Haitham as he wheeled a wooden cart carrying three of his dead cousins.

Morris reported from Mosul and Irbil. Mustafa Salim contributed to this report from Irbil.